1. (noun)reciprocal something (a term or expression or concept) that has a reciprocalrelation to something else
"risk is the reciprocal of safety"
2. (noun)multiplicative inverse, reciprocal (mathematics) one of a pair of numbers whose product is 1: the reciprocal of 2/3 is 3/2; the multiplicative inverse of 7 is 1/7
3. (noun)reciprocal cross, reciprocal hybridization involving a pair of crosses that reverse the sexes associated with each genotype
4. (adj)reciprocal, mutual concerning each of two or more persons or things; especially given or done in return "reciprocal aid"; "reciprocal trade"; "mutual respect"; "reciprocal privileges at other clubs"
5. (adj)reciprocal of or relating to the multiplicative inverse of a quantity or function "the reciprocal ratio of a:b is b:a"